Field of the Invention
The present invention relates to a control device for an internal combustion engine.
Background Art
Conventionally, as discussed, for example, in Japanese Patent Laid-Open No. 11-280505, a control device for an internal combustion engine is known that adjusts a valve overlap amount when switching between rich engine operation and lean engine operation. According to the internal combustion engine discussed in Japanese Patent Laid-Open No. 11-280505, together with calculating a deviation between a target value and an actual value of a valve overlap amount, a target air-fuel ratio is continuously switched in accordance with the deviation between the valve overlap amounts when switching between stoichiometric operation and lean operation.
Optimal control amounts for equipment (for example, a variable valve mechanism and a spark plug) of an internal combustion engine differ between a lean operation region and a stoichiometric or rich operation region. Generally, a control device controls an internal combustion engine by switching control amounts that are specified for a lean operation region and a stoichiometric or rich operation region, respectively, in accordance with maps for the respective operation regions. It is thereby possible to optimize control amounts in the respective operation regions and obtain favorable fuel consumption.
Other prior art includes Japanese Patent Laid-Open No. 2003-328809.
There are two kinds of lean combustion, namely, stratified lean combustion and homogeneous lean combustion. In comparison to an internal combustion engine that performs stratified lean combustion, an internal combustion engine that performs homogeneous lean combustion has the advantages that the amount of discharged NOx and PM are small and the costs are lower. Ideally, in an internal combustion engine that performs homogeneous lean combustion also, it is desired to change the control amounts of the internal combustion engine each time the air-fuel ratio is switched from lean to stoichiometric or from lean to rich.
After control amounts of an internal combustion engine are changed, there is a response delay until adjustment of an air intake amount and the like and adjustment of fuel injection is realized. In some cases, even when control amounts of an internal combustion engine are switched, adjustment of an air intake amount and the like that should be realized in a lean operation region occurs too late due to the aforementioned response delay. When such a situation is caused, there is the problem that there is a significant adverse effect on combustion stability during homogeneous lean combustion.